JDBC Connection Example in Java

Introduction

JDBC (Java Database Connectivity) is the standard API for connecting Java applications to relational databases such as MySQL, PostgreSQL and Oracle.

Prerequisites

• A running database server
• JDBC driver JAR on the classpath
• Valid URL, username and password

Example Program

import java.sql.*;

public class JdbcConnectionDemo {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/testdb";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT id, name FROM users")) {

            System.out.println("Connected successfully");
            System.out.println("ID\tNAME");
            System.out.println("----------------");

            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                System.out.println(id + "\t" + name);
            }
        } catch (SQLException e) {
            System.err.println("Database error: " + e.getMessage());
        }
    }
}

Sample Output

Connected successfully
ID	NAME
----------------
1	Alice
2	Bob
3	Charlie

How It Works

1. DriverManager.getConnection() opens a connection using the JDBC URL.
2. createStatement() creates a SQL executor.
3. executeQuery() runs a SELECT and returns a ResultSet.
4. Try-with-resources closes connection, statement and result set automatically.

Best Practices

• Use PreparedStatement with ? placeholders for dynamic values.
• Never embed raw user input in SQL strings.
• Store credentials in environment variables or secure config, not source code.

Common Mistakes

• Forgetting the JDBC driver on the classpath (ClassNotFoundException).
• Not closing connections in older code — always use try-with-resources.